Since Castan and Greenlee invented epoxy resin at the same time in 1936, epoxy resin has been widely used in almost all aspects of social life, such as transportation, infrastructure construction, ships and oceans, astronautics and electrical engineering, because of its good physical and chemical properties. Nevertheless, due to the flammability of common epoxy resin, it cannot meet the requirements of use in many fields. With the development of the epoxy resin industry in the direction of refinement, it has become a research hotspot to develop new and high-efficiency flame retardants to improve the flame retardancy of epoxy resins.
At present, with species diversity in epoxy resin flame retardant, practice of classification is also different. According to the elements contained in flame retardant, it can be classified into phosphorus, nitrogen, silicon, fluorine or synergistic flame retardant containing two or more elements. The retardant can be further subdivided into an additive type and a reactive type based on whether or not it has a functional group capable of reacting with epoxy resin. The reactive flame retardant has a long-lasting flame retardant effect, does not migrate in the epoxy resin, and can maintain or improve its mechanical properties while improving the flame retardancy of the epoxy resin.
Gao et al. (Gao L P, Wang D Y, Wang Y Z, et al. Polymer Degradation and Stability, 2008, 93(7): 1308-1315.) synthesized a kind of phosphorus-containing monomer DODPP with a single reactive functional group, and then DODPP in different proportions reacted with DGEBA, obtaining the epoxy resin with different phosphorus content. When the phosphorus content was 2.5%, the cured product could reach UL-94 V-0 rating and 30.2% limiting oxygen index (LOI). The values of HRR, PHRR and Av-HRR obtained by heat release test all decreased. Murias (Murias P, Maciejewski H, Galina H. European Polymer Journal, 2012, 48(4): 769-773.) synthesized two kinds of siloxanes with a terminal amino group or an epoxy group, with triethylenetetramine as curing agent and co-cured with a low molecular weight epoxy (E6) to obtain an epoxy cured product. When the amount of siloxane added was increased, the LOI value of the obtained epoxy cured product was also increased from 21.9% up to 23.9%, and the impact strength was significantly improved.